This invention relates to an improvement in mattress innerspring units and, more particularly to a means for preventing the tendency of cross helicals to spin-out or unwind from the unit.
Mattress innerspring units are generally formed of a plurality of coil springs positioned standing side by side in a plurality of substantially parallel rows. The upper and lower surfaces of an innerspring unit are defined by the terminal or end convolutions of the coil springs which convolutions are generally closed loops that may be approximately circular or be formed so as to depart from the circular configuration by having two opposed U-shaped offset portions. The coil springs in any given row are normally positioned so that their terminal convolutions are in close relationship to terminal convolutions of adjacent springs in the same row. When the coil springs are formed with offsets, the springs are positioned so that offset portions are in close relationship to the offset portions of the adjacent coil springs.
The perimeter of the unit is generally defined by border wires connected to those coil springs which are positioned at the sides of the unit. When an innerspring unit includes two border wires, they are connected respectively to the upper and the lower terminal convolutions of the springs.
Coil springs are interconnected to adjacent coil springs in the same row by means of cross helicals which are spiral coils that extend transversely of the rows of springs and lace together adjacent coil springs at their terminal convolutions. The cross helicals therefore extend across the rows of coiled springs and interconnect adjacent coil springs in both the upper and lower surfaces of the innerspring unit. Innerspring units may include a plurality of cross helicals corresponding in number to twice the number of coil springs in a row of the unit minus two. Each cross helical is incorporated into the unit by rotating it spirally about its major axis until it extends transversely of the rows and interconnects, i.e. laces together, the terminal convolutions of adjacent coil springs. Once the cross helicals are so positioned, they have a tendency to "spin-out", that is, unwind from the innerspring unit.
To eliminate this undesirable longitudinal movement of the cross helicals, it has been the practice to deform the cross helicals in various manners. The ends of the cross helicals have been distorted by bending the ends back upon themselves or forming loops such as described in U.S. Pat. Nos. 3,006,629 and 2,374,850. Cross helicals have been distorted along their lengths to provide a deformity in the spiral as described in U.S. Pat. Nos. 3,685,062 and 3,653,082. U.S. Pat. No. 2,254,106 describes a further method of preventing longitudinal movement of cross helicals by providing frictional engagement of the helicals with the coil springs. Although these methods may reduce spinout, none have completely eliminated cross helical spin-out. Further, methods for preventing spin-out by deforming the cross helicals can be reduced in effectiveness when extreme conditions of use result in further cross helical deformation.
It is desirable that cross helicals be permanently secured to a mattress innerspring unit so that any tendency of the cross helicals to spin-out or unwind from the unit is eliminated even after extended use of unit. It is further desirable to construct an innerspring unit wherein cross helical spin-out is prevented by a method of construction that does not increase the cost of construction of the unit to any appreciable extent.
It is also often desirable to increase the firmness of an innerspring unit, that is, the ratio of compression of the coil springs to unit load.
It is therefore an object of the present invention to provide a mattress innerspring construction wherein cross helical spin-out is eliminated by providing a relatively permanent means for restricting the rotation of the cross helical. It is another object of the invention to provide a mattress innerspring construction including a welding means for restricting longitudinal movement of the cross helicals. It is also an object to provide an innerspring unit with a welding means that additionally increases the firmness of the unit. It is further object to provide a method of constructing a mattress innerspring unit including a welding means to prevent at least one cross helical from spinning-out of the unit.